1. Field of the Invention
This invention relates to a method of inspecting a floppy disk comprising a magnetic disk body and a center hub which is bonded to the magnetic disk body by adhesive, and more particularly to a method of inspecting the state of application of the adhesive.
2. Description of the Prior Art
Recently, micro floppy disks such as of 3.5 inches have come into wide use as the recording medium for office automation instruments. The micro floppy disk generally comprises a magnetic disk body which is flexible and is annular in shape and a hat-like center hub bonded to the center of the magnetic disk body by adhesive. The assembly of the magnetic disk body and the center hub is housed in a hard casing. The center hub has an annular flange portion and the adhesive is applied to the flange portion of the center hub. Whether the adhesive is uniformly applied to the flange portion and whether the center hub is firmly bonded to the magnetic disk body largely affect the condition of recording reproduction of signals. Accordingly, state of application of the adhesive to the flange portion of the center core must be carefully inspected in the manufacturing process.
In one conventional method, a light beam (containing ultraviolet rays) is projected onto the adhesive layer applied to the flange portion of the center hub, the reflected part of the light beam is received by a photo detector while mechanically moving the source of the light beam and the center hub relative to each other so that the light beam scans the flange portion, thereby photo-electrically reading light information on the state of application of the adhesive, and whether application of the adhesive is in a satisfactory state is determined on the basis of the intensity of the electrical signal thus obtained. Such a method is disclosed in Japanese Unexamined Patent Publication No. 63(1988)-205867 and will be referred to as "the first conventional method", hereinbelow.
In another conventional method, the whole center hub is exposed to light containing ultraviolet rays, the reflected light is received by a charge-coupled device in an industrial TV camera, electronically scanning the charge-coupled device, thereby obtaining an electrical signal, and whether application of the adhesive is in a satisfactory state is determined on the basis of the intensity of the electrical signal thus obtained. Such a method is disclosed in Japanese Unexamined Patent Publication No. 63(1988)-205867 and will be referred to as "the second conventional method", hereinbelow.
The first conventional method is disadvantageous in that it is difficult to effect the inspection at a high speed with a high accuracy and the cost of inspection becomes high since the light beam is caused to scan the flange portion by mechanically moving the source of the light beam and the center hub relative to each other.
In the second conventional method, whether application of the adhesive is in a satisfactory state is generally determined on the basis of the number of picture elements in a predetermined window, and accordingly, the determination cannot be correctly made unless the window is positioned with an accuracy better than 0.05 mm with respect to the material to be inspected. This gives rise to a problem that the inspection cannot be effected at a high speed.